This invention relates generally to the continuous, high speed transfer of material from a carrier to a substrate, such as the hot stamping of foil in printing machines, and more particularly to high speed rotary printing machines, such as but not limited to flexographic, letterpress and rotary screen printing machines.
One form of hot stamping foil comprises a carrier or backing film and a decorative layer thereon. The decorative layer may comprise at least one layer of lacquer and optionally a layer of adhesive and other layers. For example a separation or partition layer may be provided between the backing film and the layer of lacquer, to promote separation of the decorative layer from the backing film. A metal or color layer may be disposed between the lacquer and adhesive layer.
The layers of lacquer, metal and adhesive are transferred to a substrate with heat and pressure, using a rotary brass die. The backing film may be formed of one of a number of plastic or other materials including but not limited to a polyester such as polyethylenephthalate, oriented polypropylene, polyvinyl chloride, styrene, acetate, coated and uncoated paper, cardboard, hard plastics such as polyolefins (high and low density polyethylene), polystyrene and related plastics or halogenated polyolefin polymers such as polyvinyl chloride.
Normally, rotary hot stamping is carried out using (1) a metal, usually brass, application or impression roller with raised areas configured to the shape of the desired area to be hot stamped, with the surface of such roller being heated to between 250 and 400 degrees Fahrenheit, and (2) an adjacent base or anvil roller. During the rotary hot stamping process, the layers of lacquer, metal and sometimes adhesive are separated from the carrier or backing film of the foil. In conventional rotary hot stamping, an adhesive is used and the hot stamping foil is nipped between the two rollers. In the case where an adhesive is not present on the foil, it is usually applied to the substrate in selected areas. The supporting base or anvil roller is made from vulcanized silicone rubber having a hardness of between 80 to 100 durometer, or an ebonite roller having a hardness of approximately 100 durometer. As the substrate of plastic film, paper or other sheet material to which the decoration is to be applied passes over the anvil roller, it contacts the surface of the hot stamping foil opposite the backing film. The substrate and the foil are carried together between the heated brass impression roller and the anvil roller, with the backing film facing the heated brass impression roller surface and the layers to be hot stamped or transferred facing the substrate.
An object of the present invention is to provide method and apparatus for economical, high speed continuous rotary application of material such as stamping foil to a substrate, and more particularly to the application of hot stamping foil to a substrate.
Another object of the present invention is to improve the utilization of the material, such as hot stamp foil, that is being transferred, thus to reduce the waste of such material that occurs with present machines and processes.
In accordance with the present invention, there is provided a method of continuous rotary transfer of material from a carrier to a substrate, such as hot-stamping, in which the material, such as hot stamp foil, is utilized much more efficiently than prior techniques. A method is provided whereby a carrier of the foil is both unwound from its supply roll and rewound onto a waste roll at a speed proportional to and substantially less than the speed of the substrate, while at the same time the portions of the carrier and foil in the vicinity of the nip transfer point undergo changes in velocity such that the foil is synchronous with the substrate during the actual transfer of foil from the carrier to the substrate. The apparatus and method of the present invention are extremely efficient in that they permit the continuous high speed rotary application of hot stamping foil while utilizing as much as 95% of the surface area of such foil, thereby minimizing the amount of scrap foil.
In a specific implementation, the changes in velocity are accomplished by means of a microprocessor-controlled shuttle mechanism receiving input signals from a position-sensing device indicating substrate motion, and one or more position sensors indicating the position of the raised stamping areas. A typical implementation consists of an attachment to a printing press having a continuous substrate, typically paper or plastic. The anvil and impression rollers are typically gear-driven from the press itself. The attachment is self powered independent from the press.
It is a goal of the invention, according to a specific aspect, that the process of rotary hot-stamping take place at high speeds compatible with the rate at which flexographic and similar printing presses are used, namely 100 feet/minute to 400 feet/minute. In order to effect these speeds it is desirable to keep to a minimum those portions of the foil drive which undergo velocity changes, several methods of achieving this will be described herein.
Additional objects, advantages and features of the present invention are described below with respect to its preferred embodiments, which description should be taken with the accompanying drawings.